Is the vet able to offer a phone consultation in the meantime? It took some searching, but I eventually found a vet who treats fish and is willing to provide telemedicine in my area. She understands that transporting a fish (also about an hour drive) could be too stressful for it. I actually have an introductory call with her tomorrow, so I can understand the process better in case I have any emergencies in the future and need prescription only medications.
I'm also a bit concerned about adding different medications to the tank without a clear diagnosis. I completely understand that you're frightened and trying everything possible to help Hewbie. However, mixing medications can add stress or create further problems that make it harder to diagnose the root problem here, especially since you mentioned that the other fish are now breathing somewhat harder.
Maybe I missed something, but so far I've mostly seen a poor prognosis and possible causes, without much guidance on what to actually do in the meantime. Hopefully one of the fish medics can give you clearer advice on what you should or shouldn't do until the vet appointment, so you're not left guessing.